Archive for June, 2011

Supercells with large hail and a few tornadoes possible across Midwest today

Looking back over yesterday’s major tornado outbreak from N KS into E-CNTRL NE makes me pretty sad, as I could have extended my trip for a few more days. But with such a tricky maps lately, there was nothing too interesting on the model maps until late Saturday runs. Then impressive setup was shaping up, like described in the outlook yesterday! Some very impressive and photogenic tornadoes, from stovepipes to wedges, were reported and chased by fellow US chasers! Congratulations to those who baged those beauties! Thankfully no serious damage was done to property.

After yesterday’s robust setup, a potent upper low is finally weakening and slowly shifting NE into S MN. A SFC cold front extends from SE MN/SW WI southwards across the MS valley where moderately unstable airmass lies ahead of it. Coupled with quite good moderate shear, rotating severe storms are expected mainly along/just ahead of the front later today. Supercells with threat for large hail and strong winds are the primary mode, though some tornadoes can be possible from SE MN into SW WI and across central IL where LL hodographs are the most favorable for tornadogenesis. Nicely backing ESE-erly flow should easily support LL rotating mesocyclones there.

SPC has issued a broad SLGT area from Great Lakes into the lower MS valley…

…MID/UPPER MS VALLEY THIS AFTERNOON/EVENING…

A BROKEN ARC OF LOW-TOPPED CONVECTION WILL PERSIST AND SPREAD NWD/NEWD THROUGH THE NARROW WARM SECTOR ACROSS ERN MN INTO WI THIS AFTERNOON/EVENING. THOUGH INSTABILITY IS NOT PARTICULARLY STRONG…EFFECTIVE BULK SHEAR OF 40-50 KT AND EFFECTIVE SRH AOA 250-350 M2/S2 WILL SUPPORT LOW-TOPPED SUPERCELLS CAPABLE OF PRODUCING A COUPLE OF TORNADOES. FARTHER S…INSTABILITY IS STRONGER IN THE WARM SECTOR WITH MLCAPE AOA 2000 J/KG ACROSS CENTRAL/SRN IL…WHERE DEEP-LAYER VERTICAL SHEAR ALSO FAVORS SUPERCELLS. SCATTERED CELLS/CLUSTERS WILL CONTINUE TO POSE A RISK FOR A COUPLE OF TORNADOES…IN ADDITION TO DAMAGING WINDS AND LARGE HAIL. LATER THIS AFTERNOON/EVENING…THE STORMS WILL MERGE AND SPREAD NWD/NEWD TOWARD INDIANA/SW LOWER MI WHERE STRONG INSTABILITY /AND SOMEWHAT WEAKER VERTICAL SHEAR/ COULD SUPPORT ONE OR MORE CLUSTERS WITH DAMAGING WINDS AND LARGE HAIL.

As for the chasing target, being somewhere La Crosse, WI seem fair enough for some reasonable severe storms once cap erodes in late afternoon.

Looks like quite a calm period is expected for the next days with a returning activity expected early next week. Stay tuned for the future oudates!

PDS severe thunderstorm watch is out for CNTRL OK into N TX!

Another PDS watch is out, this time a PDS severe thunderstorm watch over CNTRL OK into N OK. Intense supercells are rapidly developing along/ahead of the sharp dryline with threat for giant hail and damaging wind gusts!

Tornadoes
Probability of 2 or more tornadoes: Low (20%)
Probability of 1 or more strong (F2-F5) tornadoes: Low (5%)

Wind
Probability of 10 or more severe wind events: High (90%)
Probability of 1 or more wind events > 65 knots: High (80%)

Hail
Probability of 10 or more severe hail events: High (90%)
Probability of 1 or more hailstones > 2 inches: High (70%)

Combined Severe Hail/Wind
Probability of 6 or more combined severe hail/wind events: High (>95%)

…THIS IS A PARTICULARLY DANGEROUS SITUATION…

EXTREMELY DAMAGING THUNDERSTORM WIND GUSTS TO 80 MPH…LARGE HAIL TO 3.5 INCHES IN DIAMETER…AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.

DISCUSSION…THUNDERSTORMS SHOULD DEVELOP ALONG THE DRY LINE ON WRN EDGE OF WATCH BY 22Z. STORMS WILL RAPIDLY BECOME SEVERE GIVEN THE AVAILABLE VERY UNSTABLE AIR MASS IN ADVANCE OF THE UNSEASONABLY STRONG UPPER TROUGH . SUPERCELLS WILL BE INITIAL MODE BUT QUICKLY EVOLVE INTO LINE SEGMENTS AND BOWS. VERY LARGE HAIL ALONG WITH A POTENTIAL OF SIGNIFICANT DAMAGING WINDS WILL ACCOMPANY BOTH THE SUPERCELLS AND THE MORE LINEAR MODE THAT EVOLVES BY THIS EVENING. IN ADDITION BRIEF TORNADOS ARE POSSIBLE WITH BOTH MODES.

Stay tuned!

PDS tornado watch for N KS into E-CNTRL NE is out!

A dangerous PDS watch is out for parts of N KS into E-CNTRL KS across the warm sector as intense tornadic supercells are expected to fire ahead of the arcing dryline. Strong tornadoes becoming increasingly likely!

Tornadoes
Probability of 2 or more tornadoes: High (90%)
Probability of 1 or more strong (F2-F5) tornadoes: Mod (60%)

Wind
Probability of 10 or more severe wind events: High (80%)
Probability of 1 or more wind events > 65 knots: Mod (60%)

Hail
Probability of 10 or more severe hail events: High (>95%)
Probability of 1 or more hailstones > 2 inches: High (>95%)

Combined Severe Hail/Wind
Probability of 6 or more combined severe hail/wind events: High (>95%)

…THIS IS A PARTICULARLY DANGEROUS SITUATION…

DESTRUCTIVE TORNADOES…LARGE HAIL TO 4 INCHES IN DIAMETER… THUNDERSTORM WIND GUSTS TO 80 MPH…AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.

DISCUSSION…INTENSE SURFACE LOW OVER NCENTRAL KS WITH RAPID DESTABILIZATION OCCURRING INTO NEB WHERE SHEAR IS VERY FAVORABLE
FOR SUPERCELL DEVELOPMENT. SUPERCELL THUNDERSTORMS WELL DEVELOP AHEAD OF THE TRACK OF THE LOW WITH POTENTIAL FOR STRONG TORNADOES
INCREASING THRU THE AFTERNOON AS SYSTEM MOVES NNE. VERY LARGE HAIL ALSO LIKELY GIVEN MLCAPES AOA 2500 J/KG AND LARGE HODOGRAPHS.

*Updated at 23z with better graphics!